1. By corresponding the insolation on the open building-top to the time progress of calculated solar altitude, the amount of insolation on the earth in fine weather was estimated. Although observing value includes atmospheric change, it is concluded that insolation can be estimated sufficiently on bare land in the fine weather daytime.2. Changes of insolation in various forest stands were measured. The monthly measurement in a fine weather was so difficult that measurements were not done many times in each forest stand. On earh forest stand, 20m x 20m square plot was set, and then the insolation was measured at 1.5 meters upper site of square points at the intervals of 5 meters. PAR(photosynthetically active radiation) and luminous intensity were measured using the LI-COR LI-1000 Data Logger with a PAR sensor and a luminous sensor.3. Based on the above-mentioned idea and method, seasonal change of insolation in the forest was estimated. Consequently, the calculated parameters have made the good estimations of insolation on bare land around the forest stand possible. Concerniing the point, this research will give a new view to usual method of measuring insolation. However, because of large variation of insolation in each point, seasonal changes could not be discussed sufficiently. In addition to improving the method, further measurements are planned for accumulating data as the development of this research.